Electrical testing



Feb. 23 1926.v

J. B. JOHNSON ELECTRICAL TESTING Filed August 14. 1923 E, /ml/enfar I I l 'Johno/mson by lPatented Feb. 2 3, 1926.

yuNrrlszD STATES PATENT OFFICE.

.TOHN B. JOHNSON, F ELMHURST, NEW YORK, ASSIGNOR WESTERN ELECTRIC.

COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF YORK.

ELECTRICAL TESTING.

Application'iled August 14, 1923. Serial No. 657,422.

- To all whom it may concern:

fio

Be it known that I, JOHN B. JOHNSON, a citizen of the United States, residing at Elmhurst, in the county of Queens, State of New York, have invented certain new and useful Improvements in Electrical Testing, of which the following is a full, clear, concise, and exact description. i

The invention relates to electrical measurements, and its object is to determine hysteresis losses, especially in Aclosed magnetic circuits.

In accordance with the invention the sample is subjected to a magnetizing field increasing with time in a known manner from a maximum negative field value to a maximum positive field value, and decreasing with time from said maximum positive value to said maximum negative value, and a graph is made of the relation between the varying field and the time rate of change of the resulting induction in the sample, the hysteresis loss being determined from the area between the graph and its I-I axis in accordance with the known manner of variationof the magnetizing field withtime. ly way of example, the detailed description hereinafter sets forth means .for passing through a resistance and the magnetizing winding of thesample an alternating current increasing at a-constant time rate from a maximum negative field value to-*a maximum positive field value for a half cycle and decreasing at said rate from said maximum value to said minimumvalue` for -the remaining. half of the cycle, :the voltage across the resistance being applied across one of the orthogonally arranged pairs of deflector plates of a Braun tube and the voltage generated. in a winding on the sample due to the changing induction in the sample being applied across the other pair of de-v fiector plates, so that, as explained hereinafter, the area between the 'curve trac/ed by the beam of electrons or cathode rays of lthe tube and the H axis of the curve equals the change of induction atany time, thus enabling the plotting of the ordinary hysteresis loop the area of which is proportional to the hysteresis loss in the sample. Although in the practice of the invention .the ordinary galvanometer type of`oscil'- lograph can be used instead of the Bra-un tube or cathode ray oscillograpmithe use of the latter is preferable because with 'the galvanometer oscillograph the deflection of the moving element is produced by only ve variable, the time rate of change of induc\A tion in the sample, and consequently it is necessary to provide a moving'film or mirror Synchronized with the cyclical changes in the `magnetizing field that produces the changes of induction.

Fig. 1 of the accompanying drawings represents schematically a circuit embodying the invention; Fig. 2 is a perspective View of a rheostat employed inthe circuit of Fig.

1; Fig 3 is an ordinary type of hysteresis loop; Fig. 4 is a curve traced by an oscillograph in the circuit of Fig. 1, andrfrom which the loop of Fig. 3 maybe constructed', Fig. 5 is a diagrammatic showing of a magnetizing current supply means whichA may replace the means shown in Fig. 1 for supplying magnetizing current for the sample to be tested; and Fig. 6 "is a diagrammatic showing of a cathode ray of oscillograph indicated in the circuit of Fig. 5.

In Fig. 1 is shown a ring shaped sample 10 which has a magnetizing winding 11 of ai, turns and a secondary winding 12 of n2 turns. Magnetizing current from a source y15 comprising D. C. generators 16' and 17 is passed through a circuit from point 18 von source 15 'through a lead 19, a non-inductive resistance 20, leads 21 and `22, the winding cov4 11, a lead 23, a contact 24 movable along four resistances 25, 26, 27 and 28, through one of these resistances, through onel of-the leads 35 and 36 and one of the generators 16 and 17, back to the point 18. The magnetizing current will be regarded a positive when flowing throughll from left to right (or in other words when contact 24 is on one of the resistances 25 and 26; and as vnegative when flowing from right to left (or in other words `when contact 24 is on one of the resistances 27 and 28).

The resistances 25 to 28 are of sufficiently large values', relative to the impedances o resi-stance 20 and winding 11, to insure that, in each position of contact 24 on the resistances 25 to 28, the effect of the impedances of 2() and 11 upon the value ofthe magnetizing current is so Small as to be negligible. The contact 24` 'is preferably moved along the resistances 25 to 28 at a uniform speed. These resistances, and .the core 39 on which vthey are wound are indicated as developed in the plane of the paper in the diagrammatic showing of Fig. 1. Preferably the resistances are made in the form indicated in Fig. 2, wherein is shown a ring shaped core 39, of varying width, supported by stand 40, the resistances 25 to v28 being wound on core 39 so that the movable contact 24 can be rotated along the resistances,

as for instance by a pulley 43 and belt 44.

In order that the magnetiz'ing current I may cyclically vary at a constant time rate from a maximum negative current value to a maximum positive current Value and back to the maximum negative value as the contact 24 is continuously rotated at a constant speed each. quarter of the ring is given a width varying from point to point along the length of that quarter of the ring in accordancewvith the ordinates R of the rectangular hyperbola R=$rwhere t is thel time that contact 24 has been moving along that quarter of the ring and c is a constant equal to the voltage E of source 16 or 17 divided by k, being the desired constantrate of change of magnetizing current with the time t.; for if we call the resistance of the magnetizing circuit R (the impedances of 11 and 2O being negligible as explained above), then since it is desired to have the current increase or decrease at a constant `time rate, that is, to have the current equal kt where 7c is a constant and t is the time wlnch the'current has increased or decreased,

we have i E lE E r I==kt, RTI- E- The constant is determined as the slope of the time-current curve, or the maximuml desired value of magnetizing current divided by the time required for the contact 24 to move over any one ofthe resistances' to 28that is, over one quarter of the rmg.

The reference character 50 designates a Braun tube having two orthogonal pairs of deflector plates 51 and 52, of which one pair, say the plates 51, are connected to the' potential from a source of electro-motive force 56. A portion of the electrons yemitted from cathode 53 pass through the tubular anode 54 and between the two plates of each pair of deflector plates 52 and 51, in an electron stream `58, which forms a bright spot -on the fluorescent inner surface of the large end of the tube and serves as .a movable indicating element subject to deiection by the electro-motive forces impressed upon plates 52 and 51.

In the operation of the form of the invention shown in Fig. 1, when the contact 24 is-rotate'd the magnetizing current cyclically varies at a constant time rate, from a maximum negative current value corresponding to the value of H at the lower tip, aof an ordinary hysteresis loop such as is shown in F ig. 3, to'a maximum positive current value corresponding to the value of H at the upper tip, al, of the hysteresis loop. Forexample, when contact 24 is at its nearest point of approach on resistance 27 to thc junctions of resistances 27 and 28 the magnetizing current has its maximum negative value, this current flowing from generator 17 through lead 36, a small portion of resistanee 27, contact 24, lead 23, winding 11, leads 22 and 21, resistance 20, and lead 19, back to generator 17. As the contact 24 moves over to its nearest point of approach on resistance 28 to the junction of 27 and 28, the magnetizing current retains ,its maximum negativeyalue, the path of the current being the same as that just traced, except that from lead 36 to contact 24 it is through a small portion of resistance 28 instead of through a small portion of resistance 27. As the contact proceeds toward and reaches the free or open end of resist-y ance 28 the current approaches and reaches its minimum negative value. 1While the contact 24 is passing from 28 to 25 the current is zero. As contact 24 passes onto the free end of resistance 25 the current assumes its minimum positive value, flowing from generator 16 through elements 19, 20, 21, 22, 11, 23, 24, 25, 35, and back to 16.- As contact 24 proceeds toward the junction of 25 and 26 the current approaches its maximum positive value. As contact 24 proceeds from the junction of 25 and 26 toward the free end of 26 the current decreases to its minimum positive value. As 24 shifts to the freel end of 27 the current assumes its minivmum negative value; and as 24 again approaches the junction of 27 and 28 to complete its cycle, the current again approaches its maximum negative value to complete the current cycle.

Designating as E,L the voltage applied to the oscillograph plates 52 due to the drop caused in resistance 2O by the flow of the magnetizing current I therethrough, and

designating as 7' the. value of resistance 20,'

and designating as n, the number of turns in winding 11, we have for the value of the vlll Y as a2, we have I na'gnetiz'ing4 field Hv to which thesample isJ being` the length of the ring.

esignating as E2 'the voltage, induced/in the secondary winding 12and applied it/o/ the plates l of the oscillograplrand des gnatn4 dB dB.

ai y Kga? The. curvetraced by ythe oscillograph as a result of the ,application thereto of the volt- 'ages E1 and E2 is shown in Fig. 4, and is a derivation otra hysteresis loop Aof the ordi.-l nary type such asis shown in Fig. 3.- Beginning the magnetization cycle :at aand passing through b, c and d, the derived curve folloWsthe path a', In', c', d. Sinc the kmagnetizing field is postulated to vary with lthe time in' such a Way that H (tt) where 19 ispa constant, the area ldescribed between the derived curve-and the H axis equals the total change of induction at ali y time forl e l l The area o.A b c e is a measure of the retentivity of the material.l while `the `distance o" e between the gli? rpeak of the curvev represents the coercive force. Thehysteresis loss can vbe obtained from the derived cur-ve shown in Fig. 4 by constructing the ordinary hysteresis curve, such as that ot liig.l 3, from the .derived curve of Fig. 4 by graphic integratipn, and determining` the hysteresis loss per cycle from the constructed curve in the ordinary vvay. The construrtion of the ordinary hysteresis loop from the curve of Fig. 4 is made by taking as the value of B yfor the value axis and the oi''H at any time vthe area described between the curve ofl1`.ig.-4.and the H axis up to that valuable ,under certain` time.` f VIt shou-ld ben'oted that the osfillogra-phic method of measuring magnetic properties enables records to be` obtained in a very short time, Ivvhch is a featurel especially circumstances Which arise in practice,'a^s for instance Where large through 75 to give thel i tion current for the two tubes.'

numbers of samplesmust be tested or where it fis desired to test the changing properties o/ one sample at small time intervals.

The block t`fof Fig.' 5 may replace the i block 6() of Fig. v1 for supplying the sample with magnetizing current varying in the manner set forth above, the conductors 19 ing 11 and the resistance 20 justfas conductors 19 and 23 lead from the block 60 of Fig. 1. to winding 1l and resistance 20. In the apparatus ot the block 60 a voltage varying in the manner in which the magnetizing currentis -to vary isproduced across a condenser 65 by c vclically charging the and 23 shown as leading from block 60 ybe? mg for connection to the magnetizing'windcondensent'rom aD. C. source 67 through a constant current device such for example as a two electrode thermlonic vacuum tube 70 working a voltage Saturation (that 1s, with the electrons emitted' pass to the anode throughout. the. range of lvoltage applied to the tube), a similar vconstant current device 75, charg-- ing the condenser from a D. C. generator 80 condenser a polarity opposite to that given it by the first charge,

and discharging the condenser through 70 to'complete the cycle. The temperatures of the cathode of theitubes 7 0 and f5 should be adjusted'to give thesa'me value of satura- The chang.-

'ing of the condenser 65 from' the circuit of generator (Wand tube 70 to the circuit votl generator and tubo 75,-and vice versa. to

accomplish the charging rand dischargingof discharging the condenser through vB5 the cathode temperatureso low that all of ioe the vcondenser are effected by a commuta'tor 81 Which/ may be rotated-at any suitable speed.

The commutator is shown with a conductingsegment 82 extending around approxi# mately half of its circumference and an insulating segment extending around the other halt. The conducting segment is always in contact with the lead to the upper pla-te' of condenser 65. l/Vhen the -conducting segment contacts with the upper brush of the commutation, generator 6'? charges'the condenser'.` through tube 7()4 so` that the. upper plate of the condenser is of positive polarity with respect to the lower plate, the.c.on denser of course ytirst discharging through l67 and 70 any charge of "opposite polarity which it may have'acquired from generator- 8O. Then :if the conducting segment'be rod tated out of contact with the upper brush and into contact with the lower brush. the` current through the eondenserwillfreverse,

flowing upwardly, the voltage across the condenser and the-voltage of generator '80 acting cumulatively through ccondenser has completely discharged whcre. :upon the generator 80 continues `to send current through 'the condenser in the Aupward tube 7 5 until the i 4spect to its -upper plate.

direction to charge the condenserthrough 75 so that its lower platefisjpositive with re- When the conducting lsegment leaves the lower brush and contacts with the `\upper brush the current `through the condenser reverses, fiowing downwardly, th'evoltage l across the con-4 denser and the voltage o f generator 67 actgrid battery 87 i's shown. for adjusting the steady potential o f the gridof tube 85. The lead-2,3 -is tapped off from resistance/86 through aresistance 88 sufiiciently large', to render negligible the effect of the impedance-s of winding 11 and resistance 20 upon the ma gnetiziug current/through 11, and the.

lead 19 istapped'ofi' from generator 67' at such a point that Awhen only the voltage of battery 87 is applied to the grid of tube 85` that is, when the voltage applied to the grid of- 85 b v the condenser 65 is zero, these two tap points are at the same potential and consequentlyl the magnetizing4 current in.

winding 11 is zero. Resistance 86 is preferably suiiiciently large to cause the Aplatecurrent grid potential characteristicof tube 85 to have a constantslopepv er a consider! able working range; and the voltage of the grid battery 87 is preferably such that the normaly of the p of battery 87 vis applied to the grid, corresponds to the center of this working range'.

Vhenthe rotation of coinmutator ,'81 causes `2in-alternating voltage varying at a constant time rate to be applied to the grid of tube 85, the plate currentI 4of the tube varies at a constant time rate, above and below its normal value` and therefore there is applied to the circuit 88, 23, 11, 20, 19, an alternating volta-ge of the same wave shape, provided that the value of the resistance 88 is su'iiciently high to cause the voltage dropi in 86 due to the magnetizing' current to beso small as to introduce'no-material' dis# tortion.:

In order that the impedance .of the mag` netizing winding may-be small, it is desirable in some cases to e/mploy a i'nagneti'zing,4

current of low frequency, for instance, only 'a few cycles erl second,'or even lower.- A

` The charging or discharging of a conpklate currentvalue, that is, the value l te current when only the voltage ,sultino' induction iii thev sample.

denser through a constant 'current path, to obtain a Braun tube sweep circuit voltage varying ata constant time rate is'claimed in the Aapplication of W. A. Knoop, Serial No. 646,503; filed June 20, 1923, sweepcircuit for cathode ray oseillogra'ph, assigned to the assignee of this application.v

This invention is not limited to-varying the magnetizing'field at a constant time rate, but it 'is preferred to se varv the magneti-zing field in order to facilitate interpretationI of' the curve traced by th'e oscillograpli. l

lVhat is claimed is: l. The method of measuring hysteresis which comprises subjecting the sample to be tested to a magnetizing field varying at a constant time rate and mapping'.n the relation between the varying field and the time rate of changeof the resulting magneticiinduction in the sample.

2. The method of lmeasuring hysteresis which comprises subjecting the sample to be tested to a varying magnetizing field, and

subjecting an electron stream to ortliogonal .deflecting forces proportional respectively to said varying field and the time rate of change of the resulting induction in the sample.

3. The method of measuringhysteresis.

which comprises subjecting the sample to be tested to aniagnetizingfield varying at 'a constant time rate andsubjecting an electron stream to orthogonal electric fields proportional respectively to said varying magnetizing field and the time rate of change of the resulting induction in the sample:

x 4.. A magnetic testing system comprising,

means for subjecting the test sample to a varying electromagnetic field, and .oscillographic means for mapping the relation between said varying field and the time rate of .change of the resulting induction in the sample. A

5.y A magnetic testing system comprising means for subjecting t e test sample to an electromagnetic fieldvarying' at a constant time rate, and oscillographic means for mapping the relation between said varying field and the time rate of change of the resu-lting magnetic'in'duction in the sample.

6. Avma'gnetic testing systemcomprismg means for subjecting the test sample to a varying electromagnetic. field, indicating nieanS, and means for jsubjectingsaid indieating means to orthogonal electric fields proportional respectively to said varying field and the time rate of change of the revarying ma'gnetizing field, movable"indicating means,l and means for subjecting said indicating means to orthogonal defiecting forces proportional espectively to said varying field and the t e`rate of change ioe magnetic testing system comprising means for subjecting the test sample to aA of the resulting magnetic induction in the sample. v

8. A magnetic testing system comprising means for subjectingthe test sample to a varying magnetizing field, an oscillograph comprising a movable indicator, and means cooperating with said sample and said os- .tion produced in the sample by said varying magnetizing iield.

10. A magnetic testing system comprising means forsubjecting a test sample to a varying magnetizing lield, means for producing an electron stream, two orthogonally arranged electrostatic delecting means for controlling the direction of said stream, means for applying to one of said deflccting means a voltage proportional to said Varying magnetizing ield, and means for applying to said other deflecting means a voltage proportional to the time. .rate of change of the resulting magnetic induction in the Sample. v

11. A magnetic testing system comprising means for subjecting a test sample to a magnetizing ield varying at a constant time rate froml a maxium negative field valueI to a manimum positivefield value and varying at sald rate irom said positive value to said negative value, a Braun tube comprising two orthogonal pairs of deflect/or plates and means for passing an electron stream between each of said pairs of plates, means for applying across one of said pairs of plates a voltage proportional to said varying magnetizing field, and means -for applying across said other pair of plates avoltage. propor tional tothe time rate of change of the magnetic induction produced in the sample by said varying magnet-izing field.

12. In combination, a circuit and means for producing therein .a current varying at a constant time rate from a maximum negative current value to. a maximum positive current value,.and varying at said rate from said positive'value to said negative-value, said means comprising four impedance clements, a contact .movable along said elements, connections for including 'said contact and a variable portion of any one of said impedance elements in said circuit to vary the amo-unt of impedance introduced in said circuit by that element, and means for supplying direc-t current of one sign tosaid circuit when either of two of said impedance elements is in circuit and for supplying direct current of the opposite ,sign to said circuit when either of the other two of saidl impedance elements is in said circuit, said impedance elements each having an impedance varying in an inverse manner with the length of the element.

In Witness whereof, I hereunto subscribe my name this 2 day of August A. D.,

JOHN B. JOHNSON. 

